A solid polymer fuel cell has advantages that the operating temperature is lower and the fuel cell itself is compact as compared to fuel cells of other types, and it is expected as a promising power source for home use and automobiles for these advantages. A solid polymer fuel cell has a layered structure consisting of a hydrogen electrode, an air electrode and a solid polymer electrolyte membrane sandwiched between these electrodes. Incidentally, a fuel containing hydrogen is supplied to a hydrogen electrode and oxygen or air is supplied to an air electrode, respectively, and electric power is drawn out by oxidation and reduction reactions that occur in each electrode. Moreover, a mixture of a catalyst for promoting the electrochemical reaction and the solid electrolyte is generally applied to both electrodes.
As the catalyst constituting the electrodes described above, a noble metal, in particular a platinum catalyst supporting platinum is widely used as a catalyst metal hitherto. This is because platinum as a catalyst metal exhibits high activity upon promoting the electrode reaction in both the fuel electrode and the hydrogen electrode.
Here, the investigation cases on a platinum alloy catalyst to apply an alloy of platinum and another metal as a catalyst metal have increased in recent years in order to secure the catalytic activity while decreasing the amount of platinum used for the cost reduction of a catalyst. As the platinum alloy catalyst, a Pt—Co catalyst adopting an alloy of platinum and cobalt as catalyst particles is known as a catalyst that is able to exert higher activity than that of the platinum catalyst even though the amount of platinum used is decreased. Moreover, a ternary alloy catalyst in which a third alloying element is alloyed in order to further improve the Pt—Co catalyst has also been reported (Patent Document 1).